Automatic reset mechanism



Patented Mar. 11, 1941 UNITED STATES PATENT lOFFICE.y

Minneapolis-Honeywell Regulator Minneapolis, Minn., a corporation of Company, Delaware Application November 23, 1936, Serial No. 112,331

6 Claims.

This invention relates to automatic reset or load compensation mechanisms in general, and specifically, as applied to a follow-up system of theelectrical type.

An object of this invention is to provide a control system having a device adapted to be positioned in a plurality of positions for controlling the value of a condition, a control device the state of which is varied in accordance with changes in the value of the condition to be controlled for controlling the device, and a followup means operated by the device whereby the device is positioned in accordance with changes in the value of the condition to maintain the value of the condition within certain limits, along with a reset or load compensation mechanisnr associated with the follow-up means for causing the device to assume different positions with respect to the Value of the condition being controlled in accordance with changes in load. .drenthen object of i' is Ainvention is to provide a corno i" reset mechanism ci' advantages will become apslsilled in the art upon reference parent to those to the accompanying specication, claims and drawing.

For a more thorough understanding of this 30 invention, reference is made to the accompanying single sheet of drawing in which: Figure 1 diagrammatically discloses a preferred form; of my invention, and

Figure 2 is a sectional view of a portion of the construction illustrated diagrammatically in Figure 1.

Referring now to Figure 1 ofthedrawing, the device to be positioned in a plurality of' positions to control the value of the condition to be controlled is generally designated at I0. The control means responsive to changes in the value of the condition to be controlled is generally designated at II. The control means II controls the operation of. a relay generally this relay, in turn, controls the operation of a motor generally designated at I3. The motor I3 positions the device IU and also operates a follow-up means generally designated at I4, which follow-up means also acts upon the relay I2. to afford a follow-up control system whereby the device I is positioned in accordance with changes inv the value of the condition to be controlled to maintain the value of the condition to be controlled within predetermined limits. Associated with the follow-up means I4 is a ning desired designated at I2 and reset mechanism generally designated at I5 and the function of this .reset mechanism is to reset or reposition the device I Il with respect to the value of the condition whereby the condition to be controlled is maintained within narrower limits regardless of changes in load.

Although the control system of this invention may be utilized for controlling the value of any condition. it is shown for purposes of illustration as controlling a temperature condition and more particularly the temperature of a space (not shown). Therefore, the device I0 to be positioned in the plurality of positions is shown to be a valve IB for controlling the supply of heating uid to theLV space (not shown). The valve I6 is operated by a valve stem.I I'I which is connected by a pitman I8 to a crank disc I 9 mounted on a shaft-20 of the motor I3. Shaft 2B is driven through a reduction gear train 2l' by motor rotors 22 and 23. The motor rotors 22 and 23 are operated by eld windings 24 and 25, the arrangement being such that when the field winding 25 is energized the valve I6 is moved towards an open position and when the field winding 24 is energized the valve I6 is moved towards a closed position. Shaft 20 also carries an abutment member 23 which is adapted to open limit switches 21 and 28 when the valve I5 is moved to either an extreme open or an extreme closed position, respectively.

The control means responsive to changes in the value of' the condition to be controlled is illustrated as a thermostatic control means responsive to variations in space temperature. In this connectiorna thermostatic element 3U opcrates a slider 3I with respect to a control potentiometer resistance element 32. Upon a decrease in space temperatureyslider 3I is moved to the left in the direction indicated by the character C and upon an increase in space temperature, the slider 3I is moved to the right in the direction indicated by the character H. Preferably, when the space temperature is at the deslred'normal value, the slider 3l is maintained midway between the ends ofthe resistance element 32' in a position shown in Figure l.

The relay generally designated at I2 comprises relay coils 34 and 35 for iniiuenclng an armature 36. The armature 36 is suitably connected to a switch arm 31 which is adapted to engage contacts 38 or 39. When the relay coil 34 is energized more than the relay coil 35, the switch arm 31 is moved into engagement with the contact 33 and when the relay-coll 35 is energized more than the relay coil 34, the switch arm 31 is moved into engagement with the contact 39. When the relay coils 34 and 35 are equally energized, switch arm 31 is maintained midway between the contacts 38 and 39 and outof engagement with these contacts. Power is supplied tothe relay I2 by a step-down transformer generally designated at 43 having a primary 4I connected across line wires 42 and 43 and a secondary 44. One end of the secondary 44 is connected by a Wire 45 to the left end of the relay .coil 34 and the other end of the secondary 44 is connected by a wire 46 to the right end of the relay coil 35. The adjacent ends .of the relay coils 34 and 35 are connected together. By reason of these wiring connections, the relay coils 34 and 35 are connected in series and across the secondary 44.

A balancing potentiometer resistance element 48 is suitably secured to a base 49 (Figure 2). The shaft 20 operated by the motor I3 has loosely mounted thereon a collar 50 to which are secured spaced contacts 5I and 52. Contacts 5I and 52 are insulated from each other and from the collar 50 by insulating pads 5 3. The contacts 5I and 52 slidably engage the balancing potentiometer resistance element 43. A second collar 54 is rigidly secured to the shaft 20 by a screw 55 and this collar carries by means of insulating pads 56 a slider 51 which also slidably engages the resistance element 48. Slider 51 is located between the contacts 5I and 52. A spring member 58 is inserted between the collars 54 and 53 to hold the collar 5I! in engagement withvl friction washers 59 and since these washers also engage the stationary circuit 49, the collar 55 is frictionally held stationary with respect to the base -49 and the resistance element 48. The collar 50 is supplied with pins 60 and 6I which are adapted to be engaged by the'insulating pad 56 carrying the slider 51. Upon rotation of the shaft 20 the slider 51 is moved across the potentiometer resistance element 48 and. when the slider 51 is moved sulciently far it engages the pins 60 and 6I and overcomes the friction means to also cause movement of the slider 5| and 52. The slider' 5I and 52 form the end terminals of the balancing potentiometer and since these sliders are frictionally mounted it may be well stated that the resistance element of the balancing potentiometer is irictionally mounted. x

The left end of the relay coil 34 is connected by a protective resistance 62 and wires 63 and 64 to the left-hand end of the control potentiometer resistance element 32 and the contact 5I. In a like manner, the right-hand end of the relay coil 35 is connected by a.v protective resistance 65 and wires 66 and 61 to the right-hand end of the control potentiometer resistance element 32 and the contact 52. The junction of the relay coils 34 and 35 are connected by wires 68, 69 and 10 to the slider 3l of the control potentiometer and the slider 51 of the balancing potentiometer. By reason of these wiring connections, it is'seen'that the balancing potentiometer is formed by that portion of the resistance 48 included between the contacts 5I and 52.l It is also seenthat the control potentiometer, thebalancing potentiometer andthe series connected relay coils 34 and 35 are all connected inl parallel and across the secondary 44 of the step-down transformer 40.

Upon a 'decrease in space temperature, the slider 3I moves to the left in the direction indicated by the character C and by reason of the above noted parallel relationship this causes partial-shortv circuiting of `the relay coil 34 to decrease the energization thereof and to increase the energization of the relay coil 35. These unequal energizations of the relay coils 34 and 35 operate the armature 36 to move the switch arm 31 into engagement with the contact 39. Movement of theswitch arm 31 into engagement withthe contact 39 completes a circuit from the line wire 42, through wire 12, switch arm 31, contact 39, wire 13, limit switch 21, wire 14, eld winding 25, and wire 'l5 back to the other line wire 43. Completion oi this circuit energizes the field 25 to move the valve I6 towards an open position to supply additional heat to the space. Movement of the valve I6 also causes right-hand movement of the slider 51 of the bal? ancing potentiometer I4. This right-hand movement partially short-circuits the relay coil 35 to decrease the energization thereof and to increase the energization of the relay coil 34. When the slider 51 has moved suiiiciently far to the right so as to rebalance the relay coils 34 and 35, the switch arm 31 is moved out of engagement with the contact 39 and the valve I6 is then held in its newly adjusted position.

y An increase in space temperature causes movement of the slider 3| to the right in the direction indicated by the character H. This right-hand movement of the slider 3I partially short-circuits the relay coil 35 to decrease the energization thereof and to increase the energization of the relay coil 34. As a result of these unequal energizations of the relay coils' 34 and 35, the switch arm 31 is moved into engagement with the contact 38 to complete a circuit from theV line wire 42 through wire 12, switch arm 31, contact 33, wire 16, limit switch 28, wire 11, i'leld winding 24, and wire 'I5 back to the other wire 43. l Completion ofjthis circuit energizes the field winding 24 to move the valve I6 towards a closed position which decreases the supply of heat to the space.

Movement of the valve I6 towards a closed posi-A By` reason of the above described follow-up l control system, the valve I6; is positioned in accordance with variations in space temperature and the space temperature is maintained within predetermined limits. However, a follow-up system of this type has what is known as a drooping" characteristic, that is, when the heating load is relatively great the temperature maintained is lower than when the/heating' load is relativgly light. ing" characteristic, more heat must be supplied to the space when the heating load is great and less heat must be supplied to the space when the heatingload is light.

To accomplish this mode of operation, the re- In order to minimize this inherent droom set mechanism generally designated at I5 anddistance from the desired valve I6 is positioned normal position, the amount of which is indicated by 'the character A. Therefore, unbalancing of the relay by relatively slight deviations in space temperature within the range A will be rebalanced by the movement of the slider 51 of the balancing potentiometer within the range B and a true modulating control of the valve I6, as pointed out above, is brought about. If, however, the space temperature should decrease beyond this range designated A, the valve I6 will be moved toward an open position and the slider 5l will engage the pin 6I and since the relay is not rebalanced by this movement of the slider 5`I, the valve I6 will continue in its movement towards an open position to supply additional heat to the space to make up for the additional heating load. When sufiicient heat is supplied to the space by this additional opening of the valve I6, the slider 3l will move back into the control range A and the relay I2 will be rebalanced to stop further opening of the valve I6. Since this operation has caused right-hand movement of the sliders 5I and 52 and since the relay I2 is now balanced, the valve\|6 will be reset in a different position with respect to the value of the condition being controlled. Specically, the valve I6 will be farther towards an open position than it was before this last mentioned sequence of operation took place. increase in load on the heating system, the valve I6 is positioned farther towards an open position to supply additional heat tothe space to make up for this additional heating load.

In a like manner, if the load on the heating system decreases suiiciently to cause right-hand movement of the slider 3| of the control potentiometer out of the control range A, the slider 51 engages the pin 60 and since the slider 51' cannot rebalance the relay I2 the valve I6 is continued in its movement in the closing direction to decrease the supply of heat to the space. As a result of this decrease of the supply of heat to the space, the space temperature decreases and the slider 3| is moved back into the control range A, whereupon the relay I2 is rebalanced and further closing movement of the valve I6 is prevented. The valve I6 is in this manner reset to a new position with respect to the value of the space temperature, this new position being under the circumstances a position'closer to the closedv position to decrease the supply of heat to the space in accordance with the decrease in the load on the heating system.

By reason of the above control system, the directly in accordance with slight variations in space `temperature from the desired normal value'but when the space temperature varies a relatively large amount from the desired normal value, which variation is A caused by an increase or a decrease in the heating load, the valve I6 is reset with respect to the position of the control potentiometer` whereby the supply of heat to the space is not only regulated according. to changes in temperature but is also regulated in accordance with variations in the load on the heating system.

Although for purposes of illustration, one form of this invention has been shown, other forms thereof may become obvious to those skilled in the art upon reference to this specification and, therefore, my invention' is to be limited only by the scope of the appended claims and prior art.

I claim as my invention:

1. In combination; a device to be positioned Therefore, as a result of an 'said relay means and in a plurality of positions to control the value of a condition to be controlled, control resistance means the resistance value of which is varied in accordance with changes in the value of the condition to be controlled, relay means in control4 of said device, balancing resistance means including a resistance member and a slider member, means for operating one of the members upon operation of the device, slidable contact means engaging said balancing resistance member, connections between said control resistance means, said relay means and the slider member and contact means of the balancing resistance means, means tending to hold the contact means stationary with respect to the balancing resistance member, and means operated by said device for overcoming said last mentioned means to move the contact means with respect to said balancing resistance member.

2. In combination, a device to be positioned in a plurality of positions to control the value of a condition to be controlled, control resistance means the resistance value of which is varied in accordance with changes in the value of the condition to be controlled, relay means in control of said device, balancing resistance means including a resistance member and a slider member, means for operating one of the members upon operation of the device, slidable contact means engaging said balancing resistance member, connections between said control resistance means, the slider member and contact means of the balancing resistance means, friction means for holding the contact means stationary with respect to the balancing resistance member, and means operated by said device'for overcoming said friction means for moving the contact means with respect to said balancing resistance member.

3. In combination, a device to be positioned in a plurality of positions for controlling the value of a condition, a ,control potentiometer, m^ans for adjusting the control potentiometer in accordance with changes in the value oi the condition to be controlled, relay means for controlling the operation of said device, a balancing potentiometer comprising a resistance member, a slider member and contacts on either side of the slider member and engaging the resistance member, means for adjusting the balancing potentiometer upon operation of the device, connections between the relaymeans,the control potentiometer and the slider member and contacts of the balancing pocontacts with respect to the resistance member when they are -engaged by the slider member to cause resetting of the device to be controlled with respect to the value oi the condi'- tion to be controlled.

4. In a combined rebalancing and reset mech-` anism for a relay which controls the operation of a device, the combination of, an elongated resistance member, spaced contacts engaging said resistance member, the spacing of said contacts being less than the length of said resistance member, friction means for holding the contacts fixed with respect to the resistance member, a slider member engaging the resistance member between the contacts, and means for operating one of the members with respect to the other, said means causing movement of the contacts with respect to the resistance member upon the occurrence of a predetermined amount of relative movements between the members.

5. In combination, a device to ybe positioned in a plurality of positions 'to' control the value of 5 a condition to be controlled, control resistance means the resistance value of which is varied in accordance with changes in the value of the con- 4dition to be controlled, relay means in control of said device, balancing resistance means including a fri-ctionally mounted resistance member and a slider member contacting the same, means for operating one of the members with respect to the other upon a predetermined amount of movement of the device and for operating both members l5 upon further movement of the device in the same direction, and connections between the vcontrol resistance means, the relay means and the balancing resistance means.

. tiometer comprising a 6. in combination, a device to be positioned in a plurality of positions for controlling the value of-a condition, a control potentiometer," means for adjustingthe control potentiometer in accordance with changes in the value of the condition to be controlled, relay means for controlling the operation of .said device, a balancing potenfrictionally mounted resistance member and a slider member contacting thesame, means for operating one of the members with respect to the other upon a predetermined amount of movement of the device and for operating both members upon further move'- ment of thedevice, and connections between the relay means, the control potentiometer and the balancing potentiometer.

JOHN E. HAINES. 

